Which of the following is a white solid substance used in cosmetics?

Cetyl alcohol is a white solid substance commonly used in cosmetics, functioning primarily as an emulsifying agent and thickener. It is derived from natural sources such as coconut or palm oil and helps to stabilize formulations by creating a smooth texture that enhances the spreadability of products on the skin.

In contrast, lanolin is a waxy substance obtained from sheep's wool, which is usually yellowish and has a more greasy texture, making it less suitable for this specific description. Aloe vera is a gel-like substance known for its soothing properties, typically found in liquid form rather than as a solid, and glycerin is a clear, viscous liquid that acts as a humectant in various formulations, thus not fitting the description of a white solid. Therefore, cetyl alcohol is the most appropriate choice among the options provided.